Fix chromium warnings for SdpVideoFormat.

Bug: webrtc:163
Change-Id: I29ad3c00116692f047456df7721ba636bbb2ca89
Reviewed-on: https://webrtc-review.googlesource.com/64723
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22618}

modules/video_coding/video_coding_defines.cc

@@ -0,0 +1,23 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/video_coding/include/video_coding_defines.h"
+
+namespace webrtc {
+
+int32_t VCMReceiveCallback::ReceivedDecodedReferenceFrame(
+    const uint64_t pictureId) {
+  return -1;
+}
+void VCMReceiveCallback::OnIncomingPayloadType(int payload_type) {}
+void VCMReceiveCallback::OnDecoderImplementationName(
+    const char* implementation_name) {}
+
+}  // namespace webrtc